Electrical control system



Feba 21, 1928. f

E. R. Mcm-ON ELECTRICAL CONTROL SYSTEM Filed NQV. 19, 192

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EDMUND Rji/IORTN, OF NEW YGRK, N. Y., ASSEGNO?,

PNY, ENCOPO-RATED, 0F NEW YORK,

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nnncfrnrcnr. coivrnon x Application le. November 'lhis invention relatesto electrical control systems and particularly to a method ot andAineans for controlling the frequency oi" Wave generating devices.

.lt is applicable to the quantitative control of a characteristic ot anyelectrical circuitin which the characteristic is, or may be iliade tobe, a function kof the quantity of current iiorving in a controlcircuit, and in the operation'ot Which circuit therel occur electricalvariations having a frequency-proportional to the quantitative measureor" a characteristic to be controlled.

Une object of the invention is to generate a current in a control systemwhich varies proportionally as a quantitative measure of thecharacteristic to be controlled as above described.rvr`

Another object is to produce in the quantty of a control current avariation which is responsive to a change in relative phase ot' theelectrical variations that initiates a relative change'in theirfrequency. The re sulting comparative continuity of cause and etiecttends to increase the sensitivity oi2 the control.

lnv any system for the automatic control of a characteristic Whose valueis measured by the frequency of an electrical variation the condition otiinity or chauve o the characteristic is deter-minable onlyWith'reference to seine xed standard ofrequency. Further, the variationrelative to that stand ard niustinitiate the series oi steps culini'natiiig in the tloiv orp the required quantity ot current in the controlcircuit. lt is another object ot the invention to use as the frequencystandard a source of .electrical .variations the frequency ci which isperinanently iixed at a value correspond ng to the desired value of thecharacteristicfto be controlled, and to utilize the relative change inphase between the tivo sets ci variations to eiiect the control statedin the Erst object.

, lt is a still "further object of the invention to utilize theprinciples above announced. to control the frequency of a Wavergeneration systein and particularly to control the frey quency of sucha system. which includes the standard frequency source, itselr, as thepriinaiy frequency determining element. ln a system comprising apriinaryfrequency determining element generating small amount of potrei' and aregenerative dynainoelectric generator-anapliiier means, the princiyileof ideterniinecl by the feedback.

19, 1924. Serial llo. 750,356.'

the invention is utilized to'insure that the systein oscillates at theprimary frequency instead of at a slightly dierent frequencyk determinedby the natural conditions oit oscillation of such ampliier.

rlliese and other objects may be accomplishedin one forni of theinvention by iinpressing periodic electrical potentials derived tronithe feed-back circuit oit the'generatorainplitier, the circuit to becontrolled, on one cold electrode ot a three-electrode electricdischarge device, and separately impressing on the other cold electrodeelectrical potentials which are normally oi the same vfrequcncy but otdierent phase trom those generated by the primary frequency determiningsource, which may be a tuning :torlr l oscillatora Under normalconditions of operation an impulse ot coincidence of `positivepotentials on the two cold electrodes. lt tvill be of zero tiineduration it there is opposition of phase.

Any 'tendency toward a change or fre quency of the syst-ein as a wholetroni that which is characteristic of the primary source, as Where theregeneration is so strong that the system tends to escillate at the'frequency circuit of the L the tv/o sets of impressed h further resultsin a change -ir tne Jals during nf 'cli ere is coincidence o; positivepotentiels on both cc i successive cycles there 'l n:

. e change in the current in t current is caused f 've circuitij toconithe tendency.

is ecuivalent to that i tural frequency ot the regenerative ieVprogressive change, *per se, in i frequency and also the resultantmomentary removal or the frequency roin the immediate vicinity of itsnormal value', both to discourage tendency toward such sh' ot frequency.

il. cause en'ect condition exists between the cha ge. in relative phaseand the quantity of res ant control current. The effect has been foundto Abe greater, proportionally, than cause. The tvvo essentialconditionethat must exist in all automatic control sysa e satisfied,

J. 1 Ji" tenis ai e, inereiore,

current will flow during' the intervals intr er, results first arelative 1n this invention, the introduction of the time elementresulting from the conjoint use of two separate sets of variations, hasthe incidental eect of varying the time, rather than the amplitude,component of the control current to produce an equivalent change in thequantity of current flowing. This effect contributesl to the very greatsensitivity and quickness of control that characterizes the operation ofthe system.

The invention will be more fully understoodv from the followingdescription read in connection with the accompanying drawing, thesingle'figure of which illustrates a preferred embodiment of theinvention.

The wave generating system comprises the plrimary source 1 and thegenerator-ampli- I er 2. The generator-amplifier may be no more nor lessthan a conventional direct current generator in which alternating,instead of direct, current is supplied to the field to correspondingly.generate an alternating current in its armature circuit which reproducesin amplified form, the current which is caused to iiow through thefield. In this type of amplifier, the frequency of the output current isnot affected by the angular velocity at which the rotoris driven, butonly by the frequency of the wave impressed on the field, the outputcurrent being a reproduction, in magnified form, that wave. The energyrequired for accomlishing the amplifying effect is furnished y the rotordriving means, the amount of this energy, hence the degree of theamplification, accordingly being partially dependent on the angularvelocity of the rotor. i ln the specific system illustrated, the circuit3 is the output or armature circuit of the generator which is connectedto brushes s, the circuit being completed through armature 5 whichincludes a commutator (not shown). The magnetic field circuit of thegenerator comprises the ma netic field structure 6, armature 5, and t eair gaps between these elements. The armature is driven by electricmotor or other functionally equivalent means 7. The field is excitedprimarily by acoil 8 which derives its current, through triple windingtransformer 9, from primary source 1.

This source may be of any type which is capable of generating currenthaving a sufiiciently const-ant frequency. A tuning fork oscillator hasbeen found to be well adapted for this purpose. In the specific form oftuning fork oscillator illustrated, the prongs -of the tuning fork 10are driven by electromagnet 11 which is excited by current from source12 through resistance 13, the value of which determines the amplitude ofvibration of the fork and accordingly to some extent the operationalcharacteristics of the oscillator. The circuit through this drivingcircuit is periodically closed by the vibrationof' the right hand prongof the fork at contact 14. As the fork vibrates, the left hand prong atthe furthermost limits of its movement closes circuits at contacts 15and 1G. When contact is made at 15, a circuit is completed whichcomprises source 12, regulating resistance 17 ,'meter 18, the left handportion of the primary winding 19 of transformer 9, contact 15 and theleft hand prong of the fork. Similarly, when contact is made at 16, acircuit is closed through the `right hand portion of the primary winding19. On account of the periodic alternation of the direction of flow ofthe current through the primary winding there is generated in thesecondary winding 20 a wave which closely approximates a sine wave.Since the field coil 8 derives its current from this coil, thearrangement, there'- .fore, insures that the finally produced current inthe armature circuit 3-4-.5'is substantially of sine wave form. Circuits21 and 22, each comprising a condenser and a resistance in series, areconnected across the gaps between contacts 15 and16, respectively, andthe. fork. They tend to absorb the excess potential developed when thecircuit is broken at contacts 15 and 16 to prevent destructivesparking-.at such contacts. Meter 18 may be used to determine thenecessary setting of the resistance 17 and other elements for theefficient operation of the sys' tem.

Condenser 23 is inserted in the field coil circuit of thegenerator-amplifier. It, together with coil 8 and secondary winding 20insures that said circuit is tuned to substantially the frequency of thecurrent from the primary source, so as to provide the most effectiveutilization of the current from that source. Since the effectiveness ofthis circuit depends largely on its sharpness of tuning, it is'desirablethat it should contain 'as little resistance as possible. For thisreason, the magnetic structure 6 is preferably m'ade up of material nowwell known by the name of Permalloy. This alloy may compriseapproximately 20% of iron and 80f` of nickel which is given a specialheat treatment. This material is distinguished by the remarkably lowvalue of magnetizing current required to produce saturation and,accordingly, by its remarkably great pern'leability. These qualitiescontribute to the desired end in present system, of producing a verysmall core loss. it means an absorption of energy that would otherwisebe usefully employed, has an effect equivalent to that of a resistancein the magnetizing circuit of the material in which thelloss occurs.v

Although the arrangement of the mag:- netic structure and themagnetizing circuit therefor is disclosed in a very simple and As iswell known, coreloss, slnce aandoen partially diagrammatic' form, it isto ,be

understood that the operation 'of the invention does not`depend inanyway on Yany specific arrangement of these elements, which may conformto any of the arrangements used in conventional generator practice.Accordingly, the structure 6 may be laminated or otherwise subdivided tofurther decrease the core losses. The amplifying properties of the abovedescribed generator-amplifier are increased by feeding back a portion ofthe output current from shunt circuit 2e through a loosely coupledtransformer 25 to the eld ofthe amplifier, that is, from the output tothe input circuit of the generatonampliiier. 'The feed-back energy isimpressed on the field through coil 26 which may be wound on themagnetic tleld structure 6 or be4 otherwise related to thegenerator-'amplifier to produce an equivalent effect. ln order to maltemosteiective use of the feed-back principle, this feed-back(regenerative) circuit is preferably tuned by means of condenser 27 to afrequency asclose as is prac-f ticable to the generated frequency. Theconditions that control this adjustment and a means which rnalresvpossible a very close approximation to the generated frequency `areointed out below. l

Since the system as a whole, as so far described, has two degrees offreedom., namely, those depending on the primary frequency and thetuning of the 'regenerative circuit, the system tends to oscillate ateach of two frequencies. 'lhese two frequencies, as a practical -matterof adjustment, must necessarily differ by at least a small amount. Theeflect of this is that, although the system 'tends to oscillate moststrongly at the primary frequency and does normally so oscillate,nevertheless if the regeneration exceeds a certain critical limit, andif the frequency `of this circuitapproximates too closely the primaryfrequency, the tendency for the system to oscillate atthe frequency ofthis'circuit may overcome this normal tendency. .A shift of frequencymay therefore occur, the frequency being subsequently determined by thenatural frequency of the regenerative circuit rather than by the primaryfrequency which is more constant and which is accordingly to bepreferred as the frequency -which is characteristic of the system.

llt is the function of the controlling device 28 to prevent thisfrequency shift. rlhis device comprises an electricdischarge tube havingthe usual ilamentary cathode 29, anode 30 and control electrode 3l.Direct current sources 32, 33 and 34, respectively,

energize the cathode, provide an initial po tential biasing for thecontrol electrode, and

supply space current for the device. Electrice-l variations having thefrequency of the primary source are impressed through transformer 9 andcircuit 35 on the control electrode and cathode of the discharge device.

Although a source included in a separate `circuit may be used forsupplying the biasfor the generator-amplifier, which would tend toresult in a direct current component in the iinally generated wave, twocondensers 36 and 37 are used to separate out this component from theoutput and fed- 4baclr currents.

Vf ith the control device arranged as illusrated, and assuming that thefrequency of he system is determined by the frequency of the primarysource as under normal .conditions of operation, the phases of the tivosets of impressed electrical variations differ by an angle having somevalue between 0 and 189 electrical degrees.

Since current can flow in the anode-.cathode circuit of the device onlywhen there is coincidence of positive potentials impressed on the anodeand control electrode; there will be flow of impulse current in thiscircuit and accordingly through the rcgenerae tive' circuit, an impulseoccurring once during each cycle of the impressed variations.

' rfhis result would occur equally no unidirectional potential wereimpressed on the anode by means of the battery 34a However, the use ofthis battery, if caused to provide a positive potential for the anodewhich is not greater than the maximum negative pctentials of thevariations impressed thereon, results in a more eliicient operation ofthe device. Among other effects, insures greater average width of thecurve representing the variation of the impulse current plotted on atime scale of abscissae and accordingly a greater quantity of controlcurrent per impulse.

rfhe character of these impulse currents will be affected, as in thesimilar case of the battery 314:, by the value of the biasing controlelectrode potential. lf this potential is such as corresponds to thelower end of the static control electrode potential-anode currentcharacteristic curve, these currents can dow in the anode-cathodecircuit only, so far as affected by the control. electrode potential,during positive alternations of vimpressed alternating potentialvariations.

Y both the anode and control electrode will have positive potentialsimpressed upon them. The result will be a progressive change in theimpulse current flowing in the regenerative circuit. This tendstoprevent the shift of frequency, from that value which ischaracteristic of the current from the primary source, to a valuecorresponding preferable to make the phase angle less than 180electrical degreesto insure a change in control current in eitherdirection from the normal value that is, an' increase in one directionand a decrease in the other direction, as the shift occurs in acorrespondingT direction. The use of this expedient makes po'ssible theyextension of the 'principle' to the automatic regulation of thefrequency where the change tends to occur in eithei` direction dependingon the tuning of the regenerative circuit. If the phase angle for normaloperation iverc 180 degrees there would be a change from zero to afinite value of the control current for a change of relative phase ineither direction.

Of course the operation of the basic principles of the invention doesnot depend on the particular Wave generating system disclosed, in which,therefore, the tuned circuit typifies any circuit What-ever in whichthere may occur a. change of frequency and which is responsive tochanges in current flowing therein to correct the condition whichresults in the change in frequency.

A rigid mathematical analysis of the control phenomenaA accompanying-tliis change in impulse current is difficult and, ysince it is notrequired in order to enable one'to practice the invention, will not bemade here.

The following is offered, however, as suggestive of a proper angle ofapproach for a complete quantitative analysis of the phenomena and assuggestive of certain basic principles involved.

One definite effect of the change of current in the regenerative circuitis'a change in the natural frequency of the lregenerative circuit. Thatthis is true is evident when it is considered thatthe resistance of thiscircuit is an element in the equation express*- ing the naturalperiod.'` Achange of current in the circuit means a change in the energylosses in the circuit which is equivalent to a change in its resistanceand hence in its natural frequency.

This vchange in tuning is progressive during the time thatfthe frequencyof the system tends to vary from the primary frequency both from theprogressive continuous change in the frequency towardswhich the systemtends to shift without regard to thel value of that frequency and fromthe removal of that frequency from the-value to Which the system mosteasily tends to shift. For example, if

,the regenerative circuit were tuned too closely to the primaryfrequency, a change in its natural frequency to a value comparativelyremote from the primary frequency would tend to remove the reason forthe shift.

Having set forth the novel principles involved inthe invention anddescribed in detail a' preferred embodiment thereof, the parts,combinations, methods and apparatus believed to be newvand patentableare defined in the following claims:

What is claimed is:

il. In\combination an electric discharge device having a cathode and atleast two cold electrodes, a source of `pulsating potential, means forimpressing said pulsating potential on said cathode and one of the coldelectrodes, an independent source of pulsating potential, means forimpressing said last mentioned pulsating potential on said cathodeandanother cold electrode, and means for producing between the cathode andone of said cold electrodes current variations, said means includingmeans for changing the phase relation of the pulsating potentials.

2. In combination -an electric discharge device having a cathode and atleast tivo cold electrodes, a 'source of pulsating potential, means forimpressing said pulsating potential on said cathode, and one of the coldelectrodes, an independent source of pulsating potential, said sourcesnormally generating potentials having the same frequency, means forimpressing said second pulsating potential on the cathode, and anothercold electrode, and means for producing current variations in the pathbetween the cathode and 'one cold electrode due to phase displacementsbet-Ween the pulsating potentials.

In combination a system to be controlled, a controlling circuit for saidsystem,

,menace `trical variations on an individual pair of Y said electrodes.

4. In combinationv a system to be controlled, a controlling circuitforsaid system, means for deriving from said system elecf trical variationswhose frequency varies proportionally with the variations in thequantitative measure of a characteristic of said system to becontrolled, a lsource of standard'frequency electrical variations, anelectric discharge controlling device having a pair of input and a pairof output electrodes, the latter being included in said controllingcircuit, means for impressing said derived variations on said pair of`output electrodes, and means for impressing said standard frequencyvariations on said pair of input electrodes.

5. In combinationan electrical wave generating system .comprising 'afrequency selective circuit, means for deriving from said systemelectrical variations whose frequency varies with the frequency of thegenerated wave, a source of standardffrequency electrical variations, anelectric discharge controlling device having input and outputelectrodes, the latter being. connected to said selective circuit,'andmeans for impressing said derived and standard frequency variationsrespectively on said output and input electrodes in different relativephases, whereby when the two frequencies tend to differ an impulsecurrent whose period progressively changes from cycle to cycle tends tobe superposed on the normal current in said selective circuit.

6. In combination a system to be controlled, a controlling circuittherefor, means for deriving from said system electrical varia ationswhose frequency varies proportionally with the variations in thequantitative measure of a characteristic of said system to becontrolled, a source of standard frequency electrical variations, andmeans comprising a non-distorting electric controlling device responsiveconjointly to the variations from said deriving means and from saidstandard source to cause a. correcting current to ow through saidcontrollin circuit when the @0 two frequencies tend to' iifer.

'7. In a system Vwhich includes a circuit responsive to a change incurrent flowing therethrough the method of controlling an electricalcharacteristic of the system, which comprises generating electricalvariations of standard frequency, deriving from said system velectricalvariations Whose frequency `varies proportionally with the variations inthe quantitative measure of the characteristie to bep controlled, andcooperatively using said two sets of variations so that any relativechange in phase of said sets of variations is translated into a changeof current in said circuit.

8. n combination a regenerative amplifying device including a tunedregenerative circuit, and means responsive to a change .of frequency ofthe current traversing said circuit for preventing said device frombecoming self-oscillatory at the natural frequency of the tuned circuit.

9. A regenerative amplifying device including a tuned regenerativecircuit, and means for preventing said device from becomingself-oscillatory at the natural frequency of the tuned circuit, saidmeans comprising an electric discharge controlling device having inputand output electrodes, means connecting the output electrodes in shuntto a portion of said tuned circuit, and means for impressing on theinput electrodes potentials having a frequency different from that towhich said tuned circuit is tuned. l

10. The combination specified in claim-s 9 in which the means forimpressing potentials on the input electrodes of the device is also aprimary energy source of Waves to be amplified by said regenerativeamplif fying device.

11. ln. combination, a primary energy source, a generator-amplifierconnected thereto including a tuned regenerative circuit, and means forpreventing said system from oscillatin at a frequency determined by thenatural equency of said circuit comprising an electric dischargecontrolling device having input and output electrodes, means connectingthe output electrodes in shunt to a port10n of said tuned circuit, A andmeans for impressing on the input elecl trodes potential variationsgenerated by said primary source.

In witness whereof, l hereunto subscribe my name this 15th day ofNovember, A. D.,

